The term biology was coined in the late 1700s by the French naturalists Pierre-Antoine de Monet and Jean-Baptiste de Lamarck. It is the science of life: Of the composition and behavior of living things, of their interactions with each other and their environment.

One the central, organizing concepts in biology is that all life has descended from a common origin though a process of evolution. Charles Darwin was the first to rigorously argue this idea, which he did with his proposal of natural selection as an evolutionary mechanism. The evolutionary history of a species, i.e., the characteristics of the species from which it descended, is called the phylogeny of the species; it is studied using methods of molecular biology by analyzing biopolymer sequences of genes and proteins, and by investigating ancient forms of life in paleontology. Various methodologies have been developed, including phylogenetics, phenetics, and cladistics. An evolutionary timeline outlining the major events in the evolution of life on Earth is available.

However, this five-kingdom system is now considered by many to be outdated, and if one does not want to hyperinflate the number of kingdoms, one can use the three-domain system. These domains reflect whether cells have nuclei or not as well as differences in cell membranes / cell walls.